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Tables III and IV will be found very convenient in figuring the safe loads for beams supported at both ends, and loaded either with a distributed load or a concentrated load applied at the center.

By following the directions given, the results obtained by the use of the tables should be the same as by using the corresponding rule, and with less figuring.

When the bending or deflection of the beam is of no importance use Table III, and when excessive bending must be avoided use Table IV.

TABLE III.—STRENGTH OF HARD-PINE BEAMS.

Table of safe quiescent loads for horizontal rectangular beams of Georgia yellow pine, one inch broad, supported at both ends, load uniformly distributed. For concentrated load at center divide by two. For permanent loads (such as masonry) reduce by 10 per cent.

For beams of any width greater than 1 inch, multiply the load in table by the width of the beam in inches.

For beams of Oregon pine, use 9-10 of tabular loads; for spruce beams, 7-10; for common white pine, 3-5, and for white oak, 3-4.

To use Table III for beams that run less than the nominal dimensions. In many localities floor joists as carried in stock are more or less scant of the nominal dimensions, and for such joists a reduction in the safe load must be made to correspond to the reduction in size. For beams having the full depth multiply the load in table by the actual breadth, as 1 5/8, 1 3/4, 2 7/8, or whatever it may be. For beams 1/4 inch scant in both dimensions the safe load may be obtained by multiplying the safe load as given in the table by the following factors:

For beams 1 3/4″ × 5 3/4″ by 1.6	For beams 1 3/4″ × 11 3/4″ by 1.67
2 3/4″ × 5 3/4″ by 2.52	2 3/4″ × 11 3/4″ by 2.63
1 3/4″ × 6 3/4″ by 1 5/8	1 3/4″ × 13 3/4″ by 1.68
2 3/4″ × 6 3/4″ by 2.55	2 3/4″ × 13 3/4″ by 2.65
1 3/4″ × 7 3/4″ by 1.64	1 3/44″ × 14 3/4″ by 1.69
2 3/4″ × 7 3/4″ by 2.58	2 3/4″ × 14 3/4″ by 2.66
1 3/4″ × 9 3/4″ by 1.66	1 3/4″ × 15 3/4″ by 1.7
2 3/4″ × 9 3/4″ by 2.61	2 3/4″ × 15 3/4″ by 2.66

Example XIV.—What is the safe load for an 8 × 12 inch Georgia pine girder, of 14 feet span?

Answer.—Safe load for 1 × 12, from table = 2056 lbs. Multiplying by the breadth, 8 inches, we have 16,448 lbs. as the safe load for the girder.

Example XV.—What is the safe load for a 3 × 12 inch white pine beam of 16 feet span 1/4 inch scant in both dimensions?

Answer.—The safe load for a hard pine beam 1 × 12, 16 feet span, is given in the table as 1800 lbs. To find safe load for 2 3/4 × 11 3/4 beam, multiply by 2.63 = 4734 lbs., which is the safe load for a 2 3/4 × 11 3/4 inch hard pine beam of 16 feet span.

The strength of a white pine beam will be 3-5ths of this, or 2840 lbs.

To use Table IV for beams that are scant of the nominal dimensions:

The loads given in Table IV apply only to beams having the full depth indicated. To obtain the load for any thickness of beam, multiply the load in the table by the exact thickness of the beam, as 1 5/8, 1 3/4, 2 3/8, or whatever it may be.

For beams scant in both dimensions the correct load may be obtained by multiplying the load given in the tables by the following factors:

For 1 3/4 × 5 3/4 by 1.5	For 1 3/4 × 9 3/4 by 1.6
2 3/4 × 5 3/4 by 2.5	2 3/4 × 9 3/4 by 2.55
1 3/4 × 7 3/4 by 1.6	1 3/4 × 11 3/4 by 1.64
2 3/4 × 7 3/4 by 2.5	2 3/4 × 11 3/4 by 2.6
	1 3/4 × 13 3/4 by 1 2/3
	2 3/4 × 13 3/4 by 2.6

TABLE IV.—MAXIMUM LOADS FOR HARD-PINE BEAMS CONSISTENT WITH STIFFNESS.

Table of maximum distributed loads which can be supported by horizontal rectangular beams of Georgia yellow pine one inch broad, and supported at both ends, with safety and without deflecting more than one-thirtieth of an inch per foot of span.

For beams of any width greater than 1 inch, multiply the load in table by the width of the beam in inches.

For beams of Oregon pine, use 4-5 of tabular load; for spruce beams, 5-7, and for white pine beams, 3-5.

Example XVI.—What is the maximum load, consistent with stiffness, for a Georgia pine beam 3 × 14 inches, 24 feet span?

Answer.—The load in Table IV for a 1 × 14 beam is 1042 lbs. For 3 × 14 inch it will be 3 × 1042, or 3126 lbs.

Example XVII.—What is the maximum load, consistent with stiffness, for a white pine beam measuring 2 3/4 × 11 3/4 inches, having a span of 18 feet?

Answer.—For a 1 × 12 hard pine beam the load is 1168 lbs. For 2 3/4 × 11 3/4 inch hard pine beam multiply by 2.6 = 3037 lbs. For white pine, use 3-5ths of this, or 1822 lbs.

*In all of these rules the breadth and depth of the beam are to be measured in inches and the span in feet, the final result being in pounds.

*See Note, page 11.

†See Rule 4.

*In all of these rules the breadth and depth of the beam are to be measured in inches and the span in feet, the final result being in pounds.

*For the beam in Fig. 8 the distance L should always be measured from the support to a line passing through the center of the load, and in case of the beam in Fig. 9 the product of W and L must equal the product of W’ and L’ or if W equals W’ then L must equal L’.

*The beam shown in Fig. 11 has the same strength as that shown in Fig. 10, provided that the distance L is equal in the two cases; i.e., it makes no difference whether the cantilever end is supported by being fixed in a wall or by being balanced by an equal load on the other end of the beam.